Compositions for polyolefin foams

ABSTRACT

A foamable composition including a polypropylene-based copolymer and a polyolefin is disclosed. The composition can be used to make a stiff foam with a high closed-cell content. Methods for producing the composition and the foam are provided.

PRIORITY CLAIM

This application is a continuation of U.S. Pat. Application No.17/404,637, filed Aug. 17, 2021, which is a divisional application ofU.S. Pat. Application No. 16/293,090, filed Mar. 5, 2019, now U.S. Pat.No. 11,124,637, which claims priority, under 35 U.S.C. § 119(e), to U.S.Provisional Application No. 62/639,208, filed Mar. 6, 2018, all of whichare herein incorporated by reference in their entirety.

FIELD OF THE INVENTION

The invention relates to polyolefins generally. More particularly, theinvention relates to a foamable composition and a foam, both of whichcontain a polyolefin and a polypropylene-based copolymer. The inventionalso relates to a method of making the composition and the foam.

BACKGROUND

Polypropylene provides a balance of stiffness, chemical resistance, andheat resistance that is desirable in a wide range of applications,including food packaging and many automotive applications. Polypropylenehas a favorable environmental footprint, in part because it is readilyrecyclable. Processing polypropylene to produce a foam provides evengreater sustainability benefit by reducing material and weight. Lowdensity polypropylene foams with closed cells are typically producedusing commercially available high melt strength polypropylene.

However, there is a need for closed-cell polypropylene foams with a highclosed-cell content and higher stiffness than foams produced fromcommercially available high melt strength polypropylene. Foamspossessing these characteristics are attractive for applications such aspackaging. For example, a high closed-cell content can minimize themigration of liquids through the foam structure, thereby minimizingleakage. A high stiffness maintains the rigidity of containers filledwith liquids to avoid spills.

Therefore, there is an unmet need in the art to produce a polymercomposition that can provide closed-cell polyolefin foams with highstiffness. It is a further object of the current invention to produce aclosed-cell foam with high stiffness.

SUMMARY OF THE INVENTION

One aspect of the invention relates to a foamable composition,containing: (i) up to about 20 wt% of a polypropylene-based copolymer,based on a total weight of the foamable composition, and (ii) about 80wt% or more of a polyolefin, based on the total weight of the foamablecomposition, where the polypropylene-based copolymer has a melt flowrate of about 1 g/10 min or less and a melt strength ranging from about20 cN to about 100 cN at 190° C., the polyolefin has a melt flow rate ofabout 2 g/10 min or more, a melt strength of about 30 cN or more at 190°C., and a velocity at break of about 170 mm/s or more, and the foamablecomposition has a zero-shear viscosity of about 12,000 Pa·s or less at190° C.

Another aspect of the invention relates to a foam, comprising a polymercomposition, containing: (i) up to about 20 wt% of a polypropylene-basedcopolymer, based on a total weight of the polymer composition, and (ii)about 80 wt% or more of a polyolefin, based on the total weight of thepolymer composition, where the polypropylene-based copolymer has a meltflow rate of about 1 g/10 min or less and a melt strength ranging fromabout 20 cN to about 100 cN at 190° C., the polyolefin has a melt flowrate of about 2 g/10 min or more, a melt strength of about 30 cN or moreat 190° C., and a velocity at break of about 170 mm/s or more, thepolymer composition has a zero-shear viscosity of about 12,000 Pa·s orless at 190° C., and the foam has a density ranging from about 0.01 g/ccto about 0.20 g/cc, and a closed-cell content of more than about 80%.

Another aspect of the invention relates to a foamable composition,containing: (i) about 1 wt% to about 15 wt% of an impact copolymer,based on a total weight of the foamable composition, and (ii) about 85wt% to about 99 wt% of a polyolefin, based on the total weight of thefoamable composition, where the impact copolymer has a melt flow rate ofabout 1 g/10 min or less, the polyolefin has a melt flow rate of about 2g/10 min or more, a melt strength of about 30 cN or more at 190° C., andthe foamable composition is a blend.

Another aspect of the invention relates to a foamable composition,containing: (i) up to about 20 wt% of a long-chain branched impactcopolymer, based on a total weight of the foamable composition, and (ii)about 80 wt% or more of a polyolefin, based on the total weight of thefoamable composition, where the long-chain branched impact copolymer hasa melt flow rate of about 1 g/10 min or less, the polyolefin has a meltflow rate of about 2 g/10 min or more, a melt strength of about 30 cN ormore at 190° C., and the foamable composition has a zero-shear viscosityof about 10,000 Pa·s or less at 190° C.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure relates to a foamable composition that provideslow density closed-cell foams with substantially higher stiffness than apolypropylene foam produced with commercially available high meltstrength polypropylene. It was surprisingly found that the closed-cellcontent and the stiffness of the foam can be significantly increased bytailoring the polymer composition. Accordingly, one aspect of theinvention relates to a foamable composition containing: (a) up to about20 wt% of a polypropylene-based copolymer, based on a total weight ofthe foamable composition, (b) about 80 wt% or more of a polyolefin,based on the total weight of the foamable composition. The foamablecomposition can also include modifications, as well as other componentsone skilled in the art would typically include in a foamablecomposition.

The foamable composition can be a polymer blend. As understood by oneskilled in the art, the term “polymer” refers to a polymeric compoundprepared by polymerizing monomers, whether of the same or a differentkind. The generic term “polymer” thus includes the term “homopolymer,”which refers to polymers prepared from only one type of monomer, as wellas the term “copolymer” which refers to polymers prepared from two ormore different monomers. As used herein, the term “blend” or “polymerblend” generally refers to a physical mixture of two or more polymerswhich are not chemically combined. Such a blend may be miscible and maynot be phase separated. The polymer blend may contain one or more domainconfigurations, which are created by the morphologies of the polymers.The domain configurations can be determined by X-ray diffraction,transmission electron microscopy, scanning transmission electronmicroscopy, scanning electron microscopy, and atomic force microscopy,or other methods known in the art.

The foamable composition contains the polypropylene-based copolymer inan amount of up to about 20 wt%, or from about 5 wt% to about 20 wt%,including any ranges in between. In some embodiments, the amount of thepolypropylene-based copolymer ranges from 1 wt% to about 15 wt%, fromabout 7 wt% to about 12 wt%, or from about 8 wt% to about 11 wt%,including any ranges in between.

Conversely, the foamable composition can contain about 80 wt% or more ofthe polyolefin, or from about 80 wt% to about 95 wt%, including anyranges in between, based on the total weight of the foamablecomposition. In some embodiments, the amount of the polyolefin rangesfrom about 85 wt% to about 99 wt%, from about 88 wt% to about 95 wt%, orfrom about 89 wt% to 92 wt%, including any ranges in between.

The foamable composition has a zero-shear viscosity of about 12,000 Pa·sor less at 190° C., or from about 8,000 Pa·s to about 11,500 Pa·s. Insome embodiments, the zero-shear viscosity is about 10,000 Pa·s or less.As understood by one skilled in the art, the term “zero-shear viscosity”refers to the viscosity of the melt at a shear rate approaching to zero,and can be determined by methods known in the art such as creep recoveryexperiments.

A melt flow rate of the foamable composition can be about 11.5 g/10 minor less, about 10 g/10 min or less, or ranges from 5.9 g/10 min to about9 g/10 min, including any ranges in between. A foamable composition witha melt flow rate outside these ranges may also form a foam with thedesirable properties. In some embodiments, the melt flow rate of thefoamable composition is measured after one pass in the extruder. As usedherein, the term “melt flow rate” (MFR) (units of g/10 min) is describedaccording to and measured per ASTM D1238 using a load of 2.16 kg at 230°C.

A melt strength of the foamable composition is at least 11.5 cN, orranges from 11.5 cN to about 20 cN. A foamable composition with a meltstrength outside these ranges may also form a foam with the desirableproperties. As used herein, the term “melt strength” is an engineeringmeasure of the extensional viscosity and is defined as the maximumtension that can be applied to the melt without breaking.

The foamable composition has a velocity at break of at least about 120mm/s, at least about 140 mm/s, or at least about 160 mm/s. As usedherein, the term “velocity at break” refers to the maximum velocitybefore the melt breaks in extensional flow experiments.

Polypropylene-Based Copolymer

As used herein, the polypropylene-based copolymer refers to copolymerscontaining at least 50 wt% propylene monomer units, based on the weightof the copolymer. Polypropylene-based copolymers are typically preparedby polymerizing propylene and at least one other linear α-olefin,branched α-olefin, or cyclic olefin. The α-olefin and the cyclic olefinmay have 2 to 20 carbon atoms, 2 to 16 carbon atoms, or 2 to 12 carbonatoms, including but not limited to ethylene, 1-butene, 2-butene,1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene,3-methyl-1-pentene, 4,6-dimethyl-1-heptene, 1-octene, 1-decene,1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene,1-eicocene, norbornene, tetracyclododecene, and combinations thereof.These olefins may each contain one or more heteroatoms such as anoxygen, nitrogen, and/or silicon atom.

The polypropylene-based copolymer has a melt flow rate of about 1 g/10min or less, about 0.8 g/10 min or less, or about 0.6 g/10 min or less.The polypropylene-based copolymer has a melt strength at 190° C. rangingfrom about 20 cN to about 100 cN, from about 20 cN to about 80 cN, orfrom about 20 cN to about 60 cN. A velocity at break of thepolypropylene-based copolymer is at least about 100 mm/s, or ranges fromabout 100 mm/s to about 150 mm/s, including any ranges in between.

The polypropylene-based copolymer can be made up of linear and/orbranched polymer chains. Exemplary polypropylene-based copolymerincludes an alternating copolymer, a periodic copolymer, a blockcopolymer, a random copolymer, or an impact copolymer. In someembodiments, the polypropylene-based copolymer is a random copolymer oran impact copolymer optionally containing long chain branches. As usedherein, the term “random copolymer” refers to a copolymer in which thedifferent types of monomer units are statistically distributed in thepolymer molecules. The polypropylene-based copolymer can be apolypropylene-polyethylene random copolymer in which the content of theethylene monomer units can be up to about 7 wt%, up to about 5 wt%, orin a range of about 0.5 wt% to about 5 wt%, including any ranges inbetween, based on a total weight of the copolymer.

As used herein, the term “impact copolymer” refers to a heterophasicpolyolefin copolymer where one polyolefin is the continuous phase (i.e.,the matrix) and an elastomeric phase is uniformly dispersed therein. Theimpact copolymer includes, for instance, a heterophasic polypropylenecopolymer where polypropylene homopolymer is the continuous phase and anelastomeric phase, such as ethylene propylene rubber (EPR), is uniformlydistributed therein. The polypropylene matrix can make up from about 75wt% to about 90 wt% of the weight of the impact copolymer. The amount ofthe elastomeric phase, such as EPR, can be up to about 25 wt%, up toabout 20 wt%, up to about 12 wt%, from about 8 wt% to about 12 wt%, orfrom about 8 wt% to about 10 wt%, including any ranges in between. Theelastomeric phase contains ethylene monomer units in an amount of atleast about 5 wt%, at least about 10 wt%, at least about 25 wt%, or notmore than about 60 wt%, or in a range of about 25 wt% to about 60 wt%,including any ranges in between. The amount of ethylene in the impactcopolymer is typically not more than about 12 wt%. The impact copolymermay have a xylenes solubles content of greater than 8 wt% as determinedby acetone precipitation. The impact copolymer results from anin-reactor process rather than physical blending.

The impact copolymer may or may not be a coupled polymer, which is arheology-modified polymer resulting from a coupling reaction.Accordingly, the impact copolymer may or may not contain long chainbranches. Each long chain branch may be as long as the polymer backboneto which it is attached. Methods for detecting long chain branches areknown to one skilled in the art, for example, ¹³C NMR spectroscopy, andgel permeation chromatography coupled to a low angle laser lightscattering detector or a differential viscometer detector.

In one embodiment, the impact copolymer contains long chain branches,and can be prepared by reacting a coupling agent with a polymericprecursor such as an impact copolymer without long chain branches.

The polymeric precursor and the coupling agent can be admixed, orotherwise combined, under conditions which allow for sufficient mixingbefore or during the coupling reaction. Admixing of the polymericprecursor and the coupling agent can be accomplished by any means knownto one skilled in the art. For example, the mixing of the polymericprecursor and the coupling agent can occur in any equipment, such asV-blenders, ribbon or paddle blenders, tumbling drums, or extruders(e.g., twin screw extruders). The polymeric precursor and the couplingagent may be physically mixed by simultaneously introducing thepolymeric precursor resin and the coupling agent into the feed sectionof an extruder, such as through a main feed hopper or through multiplefeeders. Alternatively, the polymeric precursor and the coupling agentcan be added to the extruder from separate feeders. Optionally, thecoupling agent may be pre-blended (e.g., dry blended, melt-mixed) withthe polymeric precursor in a first extrusion step at a temperature belowthe reaction temperature of the coupling agent to form a masterbatch. Ina second extrusion step, the masterbatch is fed via the feed section toan extruder either separately from or together with the polymericprecursor. In some embodiments, the coupling agent is added in the formof a molecular melt with other ingredients, such as an antioxidant, tothe extruder.

During the admixing/combining, it is desirable to have as homogeneous adistribution as possible, to achieve solubility of the coupling agent inthe polymer melt, and to avoid uneven amounts of localized reactions.The coupling reaction is implemented via reactive extrusion or any othermethod which is capable of mixing the coupling agent with the polymericprecursor and adding sufficient energy to cause a coupling reactionbetween the coupling agent and the polymeric precursor. It may benecessary to activate a coupling agent with heat, sonic energy,radiation or other chemical activating energy, for the coupling agent tobe effective for coupling polymer chains. For example, the resultingadmixture can be subjected to a heating step to initiate the couplingreaction. The processing conditions (the reaction temperature, the typeof reaction vessels, the concentration of the coupling agent, andresidence times, etc.) can be varied depending on the characteristics ofthe polymeric precursor and the coupling agent. For example, thereaction temperature can range from about 190° C. to about 280° C., andthe residence time at the reaction temperature can range from 15 secondsto 90 seconds. One skilled in the art understands that a polymer (ormixtures thereof) typically melts over a temperature range rather thansharply at one temperature. Thus, alternatively, it may be sufficientthat the polymeric precursor be in a partially molten state. The meltingor softening temperature ranges can be approximated from thedifferential scanning calorimeter (DSC) curve of the polymeric precursor(or mixtures thereof).

As used herein, the coupling agent is capable of insertion reactionsinto C—H bonds of polymers. The C—H insertion reactions and the couplingagents capable of such reactions are known to one skilled in the art.The coupling agent is capable of generating reactive species (e.g., freeradicals, carbenes, or nitrenes) that couple the coupling agent with thepolymeric precursor.

In some embodiments, the coupling agent is a poly(sulfonyl azide) thatencompasses a compound having multiple sulfonyl azide groups (—SO₂N₃).The poly(sulfonyl azide) is any compound having at least two sulfonylazide groups (—SO₂N₃) reactive with the polymeric precursor. Preferablythe poly(sulfonyl azide)s have a structure represented by X—R—X, whereeach X is SO₂N₃ and R represents an unsubstituted or inertly substitutedhydrocarbyl, hydrocarbyl ether, or silicon-containing group, preferablyhaving sufficient carbon, oxygen, or silicon atoms to separate thesulfonyl azide groups sufficiently to permit a facile reaction betweenthe polymeric precursor and the poly(sulfonyl azide). For example, therecan be at least one, at least two, or at least three carbon, oxygen, orsilicon atoms between the sulfonyl azide groups. While there is nocritical limit to the length of R, each R can have less than about 50,less than about 20, or less than about 15 carbon, oxygen, or siliconatoms. Silicon containing groups include, without limitation, silanesand siloxanes.

Examples of a suitable poly(sulfonyl azide) include but are not limitedto 1,5-pentane bis(sulfonyl azide), 1,8-octane bis(sulfonyl azide),1,10-decane bis(sulfonyl azide), 1,10-octadecane bis(sulfonyl azide),1-octyl-2,4,6-benzene tris(sulfonyl azide), 4,4′-diphenyl etherbis(sulfonyl azide), 1,6-bis(4′-sulfonazidophenyl)hexane,2,7-naphthalene bis(sulfonyl azide), and mixed poly(sulfonyl azide)s ofchlorinated aliphatic hydrocarbons containing an average of from 1 to 8chlorine atoms and from about 2 to 5 sulfonyl azide groups per molecule,and mixtures thereof. In some embodiments, the poly(sulfonyl azide) isoxy-bis(4-sulfonylazidobenzene), 2,7-naphthalene bis(sulfonyl azido),4,4′-bis(sulfonyl azido)biphenyl, 4,4′-diphenyl ether bis(sulfonylazide), 1,3-benzenedisulfonyl azide, 1,4-benzenedisulfonyl azide, andbis(4-sulfonyl azidophenyl)methane, a mixture or any combinationthereof.

It is believed that other coupling agents can be used, and the couplingreaction would proceed as intended. These coupling agents includeperoxides, such as di(4-tert-butylcyclohexyl) peroxydicarbonate,di(tert-butylperoxyisopropyl)benzene,di(tert-butylperoxyisopropyl)benzene, di(4-methylbenzoyl) peroxide,dicetyl peroxydicarbonate, dimyristyl peroxydicarbonate, dicumylperoxide, dibenzoyl peroxide, diisopropyl peroxydicarbonate, tert-butylmonoperoxymaleate, didecanoyl peroxide, dioctanoyl peroxide,2,5-dimethyl-2,5-di(tert-butylperoxy) hexane,tert-butylperoxy-2-ethylhexyl carbonate, tert-amylperoxy-2-ethylhexanoate, tert-amyl peroxyneodecanoate, tert-amylperoxypivalate, tert-amyl peroxybenzoate, tert-amyl peroxyacetate,di-sec-butyl peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate,tert-butyl cumyl peroxide or combinations of these non-limitingexamples; an alkyl borane, such as triethylborane, trimethylborane,tri-n-butylborane, triisobutylborane, diethylborane methoxide,diethylborane isopropoxide, or combinations of these non-limitingexamples; azo compounds, such as azobisisobutyronitrile (AIBN),1,1′-azobis(cyclohexanecarbonitrile) (ABCN), 1,1′-azodi(hexahydrobenzonitrile), 2,2′-azodi(hexahydrobenzonitrile),2,2′-azodi(2-methylbuttyronitrile), or combinations of thesenon-limiting examples.

Polyolefin

As used herein, the polyolefin generally embraces a homopolymer preparedfrom a single type of olefin monomer as well as a copolymer preparedfrom two or more olefin monomers. A specific polyolefin referred toherein shall mean polymers comprising greater than 50% by weight ofunits derived from that specific olefin monomer, including homopolymersof that specific olefin or copolymers containing units derived from thatspecific olefin monomer and one or more other types of olefincomonomers. For instance, polypropylene shall mean polymers comprisinggreater than 50 wt% of units derived from propylene monomer, includingpolypropylene homopolymers or copolymers containing units derived frompropylene monomer and one or more other types of olefin comonomers. Thepolyolefin used herein can be a copolymer wherein the comonomer(s)is/are randomly distributed along the polymer chain, a periodiccopolymer, an alternating copolymer, or a block copolymer comprising twoor more homopolymer blocks linked by covalent bonds.

Exemplary polyolefins include those prepared from at least one of alinear α-olefin, a branched α-olefin, and a cyclic olefin, all of whichhave been described herein.

Typical polyolefins include polyethylene, polypropylene, a copolymer ofpolyethylene and polypropylene, and a polymer blend containingpolyethylene, polypropylene, and/or a copolymer of polyethylene andpolypropylene. For example, the polyolefin can be a polypropylenehomopolymer that contains more than about 99 wt% of propylene monomer.

The polyolefin may or may not be a coupled polymer. In some embodiments,the polyolefin is a coupled polymer, being the reaction product of asemi-crystalline polyolefin, such as a polypropylene homopolymer, and acoupling agent such as a poly(sulfonyl azide). The polyolefin may beprepared by methods described herein for the coupled impact copolymer(e.g, by replacing the polymeric precursor with the semi-crystallinepolyolefin) or by methods described in U.S. Pat. Application No.15/010,099, filed on Jan. 29, 2016, and assigned to Braskem America,Inc., which is incorporated herein by reference in its entirety.

The semi-crystalline polyolefin can be a homopolymer that does notcontain long chain branches. Examples of a suitable semi-crystallinepolyolefin include, but are not limited to, a polypropylene, or apolyethylene, or combinations thereof. Examples of polypropylene includebut are not limited to a polypropylene homopolymer. For example, apolypropylene homopolymer having a melt flow rate of at least 1.8 g/10min, or a melt flow rate ranging from about 15 g/10 min to about 40 g/10min, or from about 15 g/10 min to about 25 g/10 min, including anyranges in between, can be used in the present disclosure. Thecrystallinity of the semi-crystalline polyolefin can be at least 50%, orranges from about 60% to about 90%, or from about 70% to about 80%,including any ranges in between. Crystallinity can be measured bymethods known in the art such as DSC.

The content of the coupling agent, such as the poly(sulfonyl azide), isat least 500 ppm, or ranges from about 500 ppm to about 6,500 ppm, orfrom about 3,000 ppm to about 6,500 ppm, including any ranges inbetween, based on the total weight of the polyolefin.

The polyolefin has a melt flow rate of about 2 g/10 min or more, or fromabout 2 g/10 min to about 20 g/10 min. The polyolefin has a meltstrength of about 30 cN or more at 190° C., or from about 30 cN to about100 cN, or from about 30 cN to about 80 cN. The polyolefin has a meltingtemperature of at least 140° C., at least about 160° C., or from about160° C. to about 170° C. A crystallization temperature of the polyolefinis at least about 120° C., or at least about 130° C. The melting andcrystallization temperatures of the polyolefins can be measured bymethods known in the art such as differential scanning calorimetry(DSC).

The polyolefin has a melt drawability of at least about 170 mm/s, orabout 170 mm/s to about 250 mm/s. A flexural modulus of the polyolefinis greater than about 240,000 psi, or ranges from about 240,000 psi toabout 350,000 psi. As used herein, the term “flexural modulus” isdescribed according to and measured per ASTM D790. The polyolefin has aheat distortion temperature under load of 66 psi (DTUL@ 66 psi) greaterthan 101° C. and typically not more than 120° C. As used herein, theterm “heat distortion temperature under load (DTUL)” is describedaccording to and can be measured per ASTM D-648. The polyolefin has aratio of melt strength to melt flow rate of greater than 18 andtypically not more than 100.

The foamable composition typically further comprises a filler (e.g.,wood, silica, glass, clay, and other polymers), an additive (e.g., anucleating agent), or both.

The foamable compositions of the present invention can include anyconventional plastics additives in any combination. The amount shouldnot be wasteful of the additive. Those skilled in the art ofthermoplastics compounding, with reference to such treatises as PlasticsAdditives Database (2004) from Plastics Design Library(www.elsevier.com), can select from many different types of additivesfor inclusion into the compounds of the present invention.

Non-limiting examples of additives or oligomers are adhesion promoters;antioxidants (e.g., antioxidants containing thioether, phosphite, orphenolic units); flame retardants; biocides (antibacterials, fungicides,and mildewcides); anti-fogging agents; anti-static agents; bonding,blowing and foaming agents; dispersants; fillers (e.g., glass fibers)and extenders; smoke suppressants; expandable char formers; impactmodifiers; initiators; acid scavengers; lubricants; micas; pigments,colorants and dyes; plasticizers; processing aids; other polymers;release agents; silanes, titanates and zirconates; additional slipagents; anti-blocking agents; stabilizers such as hindered amine lightstabilizers; stearates (e.g., calcium stearate); ultraviolet lightabsorbers; viscosity regulators; waxes; antiozonants; organosulfurcompounds; nucleating agents (e.g., talc); and combinations thereof.

Antiblock additives are often used together with slip additives and fortheir complementary functions. Antiblock additives reduce adhesion orthe “stickiness” between polymer layers (usually layers of the samepolymer), which is created by blocking forces inherent to many polymers.Whereas slip additives decrease friction caused from moving across thesurface of a polymer, antiblock additives create a microrough surfacethat lessens the adhesion caused by these blocking forces. Antiblockadditives, like slip additives, are commonly used to improve thehandling of a polymer for applications such as packaging. For instance,a non-migratory antiblock additive, such as crosslinked poly(methylmethacrylate) or inorganic silica, can be used.

Method for Producing the Foamable Composition

The polypropylene-based copolymer and the polyolefin can be dry-blendedin a gravimetric mixing feeder. The resultant mixture can be fed to anextruder and then extruded by means known in the art using the extruder(or other apparatus). Alternatively, the polypropylene-based copolymerand the polyolefin can be added separately to the extruder and themixing of the polymers occurs in the extruder. The term “extruder” takeson its broadest meaning and includes any machine suitable for polyolefinextrusion. For instance, the term includes machines that can extrudepolyolefins in the form of powder or pellets, sheets, fibers, films,blow molded articles, foams, or other desired shapes and/or profiles.Generally, an extruder operates by feeding material through the feedthroat (an opening near the rear of the barrel) which comes into contactwith one or more screws. The rotating screw(s) forces the materialforward into one or more heated barrels (e.g., there may be one screwper barrel). In many processes, a heating profile can be set for thebarrel in which three or more independentproportional-integral-derivative controller (PID)-controlled heaterzones can gradually increase the temperature of the barrel from the rear(where the plastic enters) to the front.

The vessel can be, for instance, a single-screw or a twin-screwextruder, or a batch mixer. Further descriptions about extruders andprocesses for extrusion can be found in U.S. Pat. Nos. 4,814,135;4,857,600; 5,076,988; and 5,153,382; all of which are incorporatedherein by reference.

After extrusion, the foamable composition can be solidified, optionallypelletized and stored, transported, and then re-heated with a blowingagent and foamed at any time after the composition is produced.

Foam

Another aspect of the invention relates to a foam, comprising a polymercomposition, containing: (i) up to about 20 wt% of thepolypropylene-based copolymer, based on a total weight of the polymercomposition, and (ii) about 80 wt% or more of the polyolefin, based onthe total weight of the polymer composition, where the foam has adensity ranging from about 0.01 g/cc to about 0.20 g/cc, and aclosed-cell content of more than about 80%.

Foams have a cellular core structure created by the expansion of ablowing agent. A blowing agent is a substance which is capable ofcreating voids in a polymer matrix thereby producing a foam. The blowingagent can be a physical blowing agent, a chemical blowing agent, orboth. Exemplary physical blowing agents include liquefied hydrocarbons(e.g., pentane, isopentane, cyclopentane, butane), liquid carbondioxide, nitrogen, hydrochlorofluoroolefins (e.g.,1-chloro-3,3,3-trifluoropropene, 2-chloro-3,3,3-trifluoropropene, anddichloro-fluorinated propene), hydrofluoroolefins(3,3,3-trifluoropropene, 1,2,3,3,3-pentafluoropropene, cis- and/ortrans-1,3,3,3-tetrafluoropropene, and 2,3,3,3-tetrafluoropropene), andcombinations thereof. An amount of the physical blowing agent can be upto 1 wt%, including any fraction ranges in between, based on a totalweight of the polymer composition. Chemical foaming agents (CFAs)release gasses upon thermal decomposition. Exemplary chemical blowingagents include azo compounds (e.g., azodicarbonamide), hydrazinederivatives (e.g., p-toluenesulfonylhydrazide, p,p′-oxybis(benzenesulfonylhydrazide), benzenesulfonyl hydrazide, p-toluenesulfonylacetone hydrazone), carbazides (e.g., p-toluenesulfonylsemicarbazide,p,p′-oxybis (benzenesulfonylsemicarbazide)), tetrazoles (e.g.,5-phenyltetrazole), nitroso compounds (e.g.,N,N′-dinitroso-pentamethylenetetramine), carbonates (e.g., sodiumbicarbonate), those sold under trade names of SAFOAM®, HYDROCEROL®, andECOCELL®, or any combinations thereof. An amount of the chemical blowingagent can be up to 0.10 wt%, including any fraction ranges in between,based on the total weight of the polymer composition.

The foam structure has at least two phases, a polymer matrix and voids.The foam described herein has a closed-cell structure. In closed-cellfoams, the voids are completely enclosed by cell walls and the voids arenot interconnected with other voids by open passages. The foam has aclosed-cell content of more than about 80%, more than about 85%, or morethan about 90%. The closed-cell structure can be determinedqualitatively by dipping a sample of the foam strand into a solution ofisopropanol and dye. Closed cells are indicated if the alcohol/dyesolution does not penetrate the foamed sample. Alternatively, thecontent of closed-cell can be determined using a pycnometer orindirectly from the ASTM D6226 method.

The foam has a cell count ranging from about 1.0 million cells/inch³ toabout 2.0 million cells/inch³, or from about 1.2 million cells/inch³ toabout 1.7 million cells/inch³. The cell count can be obtained by methodsknown in the art, for example, by calculating the number of cells in anunit area in an optical micrograph.

The polymer composition is capable of being used to make a low densityfoam having any suitable density, which may be in the range from about0.005 g/cc to about 0.60 g/cc, from about 0.01 g/cc to about 0.20 g/cc,or from about 0.10 g/cc to about 0.20 g/cc.

The foam has a shear modulus (i.e., foam modulus) of about 12,000 Pa ormore and typically not more than 20,000 Pa at 20° C. In someembodiments, the foam has a shear modulus of 2,500 Pa or more andtypically not more than 5,000 Pa at 100° C. As understood by one skilledin the art, the term “shear modulus” describes the response of thematerial to shear stress, and is defined as the ratio of shear stress tothe shear strain. Shear modulus is also commonly referred to as themodulus of rigidity. The shear modulus is measured by methods known toone skilled in the art, for example, dynamic mechanical analysis andASTM D4065.

The foam disclosed herein exhibit unexpected improved propertiesincluding but not limited to high closed-cell content and high rigidity.

Method for Producing the Foam

The foam can be prepared with a single extrusion in an extruder such asone or more single-screw extruders or a twin-screw extruder. In someembodiments, the pelletized foamable composition is blended with any ofthe fillers and/or additives listed herein, and/or melted at anincreased temperature before the blowing agent is added.

In other embodiments, the copolymer, polyolefin, and the blowing agentcan be preblended in a gravimetric feeder and then fed to the extruder.In some embodiments, the extruder has a cooling barrel extension and anintegrated static mixer. The total L/D ratio can be at least 40,although other ratios are possible. The extrusion throughput can be atleast 22 kg/hr, although higher or slower throughputs are possible. Theresultant mixture can be combined with a physical blowing agent, such asliquefied carbon dioxide, in an extruder fitted with a die. The extrudermelts the mixture and mixes it with the physical blowing agent. Theresulting melt mixture would then be extruded through the die. Apressure drop at the die would provide for expansion of the blowingagent(s), and the polymer composition would form a foam. Optionally, thedie geometry could provide for a foamed strand or a foamed sheet to beproduced. In the case of an annular die, the foam could be drawn over amandrel, then cooled and slit. The diameter of the annular die can be atleast 50 mm, although larger or smaller diameters are possible,depending on the desired size of the foam. A ratio of the die diameterto the mandrel diameter can be at least 2:1, although other ratios arepossible.

A sheet or a fabricated article comprising the polymer compositionhaving a resulting foam structure can be made following the foamingstep. The sheet or the fabricated article can be used in packaging,automotive, and insulation applications. Examples of a fabricatedarticle include but are not limited to thermoformable, foamed films andsheets, lightweight packaging trays, beakers and containers,microwaveable food packaging, technical foams for automotiveapplications such as headliners, carpet backing, door liners, parcelshelves, water shields, under-the-hood acoustic panels, cushioning andprotective packaging, and thermal and acoustic insulation, and any othersuitable article or combination thereof.

Another aspect of the invention relates to a foamable composition,containing: (i) about 1 wt% to about 15 wt% of an impact copolymer,based on a total weight of the foamable composition, and (ii) about 85wt% to about 99 wt% of a polyolefin, based on the total weight of thefoamable composition, where the impact copolymer has a melt flow rate ofabout 1 g/10 min or less, the polyolefin has a melt flow rate of about 2g/10 min or more, a melt strength of about 30 cN or more at 190° C., andthe foamable composition is a blend. A foam containing such acomposition can have a density ranging from about 0.01 g/cc to about0.20 g/cc and a closed-cell content of more than about 90%.

Another aspect of the invention relates to a foamable composition,containing: (i) up to about 20 wt% of a long-chain branched impactcopolymer, based on a total weight of the foamable composition, and (ii)about 80 wt% or more of a polyolefin, based on the total weight of thefoamable composition, where the long-chain branched impact copolymer hasa melt flow rate of about 1 g/10 min or less, the polyolefin has a meltflow rate of about 2 g/10 min or more, a melt strength of about 30 cN ormore at 190° C., and the foamable composition has a zero-shear viscosityof about 10,000 Pa s or less at 190° C. A foam containing such acomposition can have a density ranging from about 0.01 g/cc to about0.20 g/cc and a closed-cell content of more than about 90%.

Additional aspects, advantages and features of the invention are setforth in this specification, and in part will become apparent to thoseskilled in the art on examination of the following, or may be learned bypractice of the invention. The inventions disclosed in this applicationare not limited to any particular set of or combination of aspects,advantages and features. It is contemplated that various combinations ofthe stated aspects, advantages and features make up the inventionsdisclosed in this application.

EXAMPLES

The following examples are given as particular embodiments of theinvention and to demonstrate the practice and advantages thereof. It isto be understood that the examples are given by way of illustration andare not intended to limit the specification or the claims that follow inany manner.

Foamable Composition

The foamable compositions containing polymer A and polymer B aresummarized in Table 1. Polymer A is a high melt strength modifiedpolypropylene homopolymer produced by reacting polypropylene with apoly(sulfonyl azide). Polymer B is a polypropylene-based copolymer,which can be a random copolymer (RCP), an impact copolymer (ICP), or along-chain branched impact copolymer (LCB-ICP). Following the weightpercentages listed in Table 1, appropriate amounts of the polymerpellets were dry-blended with additives in a gravimetric mixing feeder.The resultant mixture was melted in an extruder and then extruded.

Zero-Shear Viscosity

The zero-shear viscosity of the foamable composition was measured usingan Anton Paar MCR 501 rheometer with a 25-mm 6 ° cone and plate fixture.Samples were tested using a 0.445-mm gap and allowed to equilibrate at200° C. for 10 minutes. A creep recovery experiment was run in stresscontrolled mode. A force of 100 Pa was applied for 500 s and the samplestrain was recorded. The force was stopped and sample allowed to recoverfor 1200 s.

The zero-shear viscosity was calculated from the creep phase using:

$\eta = \frac{t \ast \tau}{\sigma}$

where η is the viscosity of the material, t is time, τ is the shearstress, and σ is the strain on the material taken when t/σ reachedsteady state.

Melt Flow Rate

As used herein, the term “melt flow rate” (MFR) (units of g/10 min ordg/min) is described according to and measured per ASTM D1238 using aload of 2.16 kg at 230° C.

Rheotens Melt Strength

The extensional flow of the polymer melt was characterized using aGöttfert Rheotester 2000 capillary rheometer equipped with a Rheotens71.97 set-up. The analysis determines the resistance of the polymer meltto stretching (i.e., melt strength) and its extensibility in a giventest condition.

A 12-mm capillary barrel was used at a barrel temperature of 190° C. Themolten polymer was soaked at the test temperature for 5 minutes prior tothe test. A polymer strand was pushed through a 20-mm/2-mm L/D capillarydie with a 180 ° entrance angle at an apparent wall shear rate of about86 s⁻¹. The polymer strand was then fed into the Rheotens unit andgrabbed by two sets of two wheels. The wheel speed was adjusted toreduce the acting force on the polymer strand to approximately zero.Once steady-state was achieved, the speed of the counterrotating wheelswas continuously increased, which deformed the polymer strand untilfracture and/or slippage. The polymer strand resistance force todeformation was measured by the Rheotens unit. The peak force recordedduring the drawing process is referred to as “melt strength.” The peakvelocity is referred to as “velocity at break.”

Foam Extrusion

Polymer pellets were dry-blended with other additives using a4-component, gravimetric mixing feeder. ECOCELL® 20P, supplied byPolyfil, was added as a chemical blowing agent (0-0.10 wt%).

The foam extrusion system consists of a single screw extruder with acooling barrel extension and an integrated static mixer to provide atotal extruder L/D = 40. Extrusion throughput rate was 22 kg/hr. Liquidcarbon dioxide (1 wt%) was used as a physical blowing agent and addeddirectly to the extruder barrel through a positive displacement pump.

The extruder was fitted with a 50-mm annular die, and the extrudate wasstretched over a mandrel and then slit. The ratio of die diameter tomandrel diameter (blow up ratio) was 2:1.

Density Measurement

Density, ρ, was determined by using a 100-mm² square piece of sample.The mass (m) measured on an analytical balance was divided by the volumecalculated from the dimensions, length (l), width (w) and height (h) ofthe sample measured with a caliper, according to the equation:

$\rho = \frac{m}{l\mspace{6mu} w\mspace{6mu} h}$

Closed-Cell Content

The closed-cell content was measured using a Quantichrome Ultrafoam1200e pycnometer (V5.04). Each sample was cut into three pieces with anapproximate area of 3-inch². The exact dimensions of the pieces weremeasured by a caliper and entered into the equipment to calculate thetotal volume, V_((geometric)).

First, the mass of N₂ gas required to stabilize the pressure of an emptycylinder of known volume to 3 psig was measured. This was thecalibrating amount of gas. Then, the sample was placed in the cylinder,the cylinder sealed, the calibrating amount of gas was introduced, andthe resulting pressure was measured. The pressure difference between theempty cylinder and the cylinder holding the sample is proportionallyrelated to the volume occupied by the closed cells of sample present,V_((pycnometer)), because the gas diffuses into the open cells. Theclosed-cell content was calculated according to the expression:

$\% Closed\mspace{6mu} cell = \frac{V_{(\text{pycnometer})}}{V_{(\text{geometric})}} \times 100$

Cell Count

Foam cell morphology was analyzed through high definition imagesacquired using an optical microscope (Hirox) with magnification at 35Xor 50X, depending on the cell density. A small sample of foamed sheetwas cut with a surgical blade along a diagonal relative to the machinedirection. The cut surface was colored using a blue ink marker toenhance visual contract, and the sample was placed on the microscopestage. The micrograph area, A (µm²), and cell count, N_(A), wererecorded. The number of cells per unit area, N_(A), was used tocalculate the number of cells per volume, N, using this equation:

Modulus of Foam

The mechanical responses of polymer foams were measured over a broadrange of temperatures using dynamic mechanical analysis (DMA). Sampleswere tested in shear mode using a DMA Q800 instrument produced by TAInstruments. Foamed sheets were cut to test pieces with an area of 10mm². Two equal-size pieces of the same material were sheared between afixed and moveable plate at a strain of 0.1% as temperature wasincreased from -100° C. to +150° C. The shear modulus, G′, was reportedas a function of temperature.

The dynamic mechanical properties of the foamed PP sheets were measuredin shear using an RDA III rheometer (TA Instruments) outfitted with atorsion/rectangular fixture. All of the samples were die-cut parallel tothe machine direction (MD). In addition, a sample was analyzed in thetransverse direction (TD). Data were collected over the temperaturerange using a 3° C./minute heating rate and a 1 Hz deformationfrequency. All measurements were made in a dry nitrogen environment.While a formal error analysis was not performed on these samples, basedon historical data on homogeneous samples, the dynamic moduli areestimated to be accurate to within ± 10%.

Properties of the Foamable Composition and the Foam

The experimental results for the foamable composition and the foam arepresented in Table 1. The properties of each polymer are shown in Table2.

Comparative Example 1 is polymer A, which is a high melt strengthpolypropylene. Inventive Example 1 is a blend of polymer A with 10% of arandom copolymer (RCP). Comparative Example 2 is a blend of polymer Awith 20% RCP. Inventive Example 2 is a blend of polymer A with 10% of along-chain branched impact copolymer (LCB-ICP). Inventive Example 3 is ablend of polymer A with 20% LCB-ICP. Inventive Example 4 is a blend ofpolymer A with 10% of an impact copolymer (ICP). Comparative Example 3is a blend of polymer A with 20% ICP.

Table 1 shows that all polymer blends (Inventive Examples 1-4 andComparative Examples 2 and 3) have higher melt strengths thanComparative Example 1. Inventive Examples 1-4 have lower zero-shearviscosities than Comparative Examples 2 and 3.

All foams containing the polymer blends are stiffer (as shown by thehigher foam moduli) than Comparative Example 1 at 20° C. Further,Inventive Examples 2 and 4 are stiffer than Comparative Example 1 at100° C. Inventive Examples 1-4 have closed-cell contents of more than80%, which are higher than the closed-cell contents of ComparativeExamples 2 and 3. Further, Inventive Examples 2 and 4 have closed-cellcontents of at least 90%, which are higher than the closed-cell contentsof Inventive Examples 1 and 3.

TABLE 1 Experimental data for inventive and comparative examples thatinclude foamable compositions and foams Example Comp Ex 1 Invention Ex 1Comp Ex 2 Invention Ex 2 Invention Ex 3 Invention Ex 4 Comp Ex 3 PolymerPolymer A Polymer A + 10% RCP Polymer A + 20% RCP Polymer A + 10%LCB-ICP Polymer A + 20% LCB-ICP Polymer A + 10% ICP Polymer A + 20% ICPComposition wt% Polymer A 100 90 80 90 80 90 80 wt% Polymer B 0 10 20 1020 10 20 Velocity at break (mm/s) 224 166 169 173 167 169 165 Final meltstrength (cN) 11.3 12.3 14.7 13.2 12.4 11.7 12.1 Zero-shear viscosity at190° C. (Pa·s) 6250 11180 17294 8192 10685 8707 12335 Melt flow rateafter blending* (g/10 min) 11.4 6.2 3.7 8.1 5.9 7.7 5.8 Foam PropertiesFoam density, g/cc 0.17 0.20 0.27 0.19 0.19 0.18 0.21 Foam cell count,million cells/in³ 1.0 1.4 3.1 1.3 1.7 1.3 1.06 % closed cells in foam 9483 35 92 84 90 33 Foam modulus G′ at 20° C. (Pa) 8276 10345 13793 1379312414 12414 17241 Foam: modulus G′ at 100° C. (Pa) 2069 2069 3207 27391931 2759 3793 Comments Baseline Low closed-cell content Low closed-cellcontent * Melt flow rate measured after one pass in the extruder

TABLE 2 Properties of each polymer prior to blending Polymer Polymer APolymer B RCP LCB-ICP ICP Melt flow rate (g/10 min) 2.5 0.5 0.5 0.5 wt%ethylene propylene rubber 0 0 10 10 Melt strength (cN) 48 49 59.5 23.3Velocity at break (mm/s) 178 106 133 110

We claim:
 1. A foamable composition, comprising: about 5 wt% to about 20wt% of a polypropylene-based copolymer, based on a total weight of thefoamable composition, and about 80 wt% to about 95 wt% of a polyolefin,based on the total weight of the foamable composition, wherein thefoamable composition has a zero-shear viscosity of about 12,000 Pa·s orless at 190° C.
 2. The foamable composition of claim 1, wherein thefoamable composition further comprises a filler, an additive, or both.3. The foamable composition of claim 1, wherein the foamable compositionhas a melt flow rate of about 11.5 g/10 min or less.
 4. The foamablecomposition of claim 3, wherein the foamable composition has a melt flowrate of about 5.9 g/10 min to about 9 g/10 min.
 5. The foamablecomposition of claim 1, wherein the foamable composition has azero-shear viscosity of about 10,000 Pa·s or less at 190° C.
 6. Thefoamable composition of claim 1, wherein the polypropylene-basedcopolymer has a melt flow rate of about 1 g/10 min or less.
 7. Thefoamable composition of claim 6, wherein the polypropylene-basedcopolymer has a melt flow rate of about 0.6 g/10 min or less.
 8. Thefoamable composition of claim 1, wherein the polypropylene-basedcopolymer has a melt strength ranging from about 20 cN to about 100 cNat 190° C.
 9. The foamable composition of claim 1, wherein thepolypropylene-based copolymer is a random copolymer or an impactcopolymer optionally containing long-chain branches.
 10. The foamablecomposition of claim 9, wherein the polypropylene-based copolymer is arandom copolymer.
 11. The foamable composition of claim 9, wherein thepolypropylene-based copolymer is an impact copolymer.
 12. The foamablecomposition of claim 11, wherein the impact copolymer contains longchain branches.
 13. The foamable composition of claim 11, wherein theimpact copolymer comprises up to about 20 wt% ethylene propylene rubber.14. The foamable composition of claim 1, wherein the polyolefin has amelt flow rate of about 2 g/10 min or more.
 15. The foamable compositionof claim 1, wherein the polyolefin has a melt strength of about 30 cN ormore at 190° C.
 16. The foamable composition of claim 1, wherein thepolyolefin has a velocity at break of about 170 mm/s or more.
 17. Thefoamable composition of claim 1, wherein the polyolefin is a reactionproduct of: a semi-crystalline polypropylene homopolymer having acrystallinity of at least 50%, and at least 500 ppm of a poly(sulfonylazide), based on a total weight of the polyolefin, wherein thepolyolefin has a flexural modulus greater than about 240,000 psi. 18.The foamable composition of claim 17, wherein the polyolefin has a heatdistortion temperature under load of 66 psi greater than 101° C.
 19. Thefoamable composition of claim 17, wherein the polyolefin has a ratio ofmelt strength to melt flow rate greater than
 18. 20. The foamablecomposition of claim 17, wherein a content of the poly(sulfonyl azide)ranges from 500 ppm to 6,500 ppm, based on the total weight of thepolyolefin.